Ignacio Negueruela, Amparo Marco, Artemio Herrero, Simon Clark
备注：
Accepted for publication in Astronomy & Astrophysics (Jun 13th). One long table will appear only in electronic format. Figure 8 will be published electronically and appears with reduced quality
The compact association Cygnus OB2 is known to contain a large population of massive stars, but its total mass is currently a matter of debate. While recent surveys have uncovered large numbers of OB stars in the area around Cyg OB2, detailed study of the optically brightest among them suggests that most are not part of the association. We observed an additional sample of optically faint OB star candidates, with the aim of checking if more obscured candidates are correspondingly more likely to be members of Cyg OB2. Low resolution spectra of 9 objects allow the rejection of one foreground star and the selection of four O-type stars, which were later observed at higher resolution. In a subsequent run, we observed three more stars in the classification region and three other stars in the far red. We identify five (perhaps six) new evolved very massive stars and three main sequence O-type stars, all of which are likely to be members of Cyg OB2. The new findings allow a much better definition of the upper HR diagram, suggesting an age ~2.5Myr for the association and hinting that the O3-5 supergiants in the association are blue stragglers, either younger or following a different evolutionary path from other cluster members. Though the bulk of the early stars seems to belong to an (approximately) single-age population, there is ample evidence for the presence of somewhat older stars at the same distance. Our results suggest that, even though Cyg OB2 is unlikely to contain as many as 100 O-type stars, it is indeed substantially more massive than was thought prior to recent infrared surveys.
Stellar tracers of the Cygnus Arm. II: A young open cluster in Cam OB3
Cam OB 3是唯一被认为属于外银河臂或天鹅座臂的OB星协。很少有成员被观测到，并且对该星协的距离模数也不清楚。我们试图更完整地描述凸轮OB 3的人口和更好地确定其距离模量。我们目前的紫外测光的O-型恒星BD +56 864和LS I +57 138周围的区域，发现一个明确的序列的早期类型的恒星，定义了一个未编目的疏散星团，我们称之为阿利坎特1。我们还提出了光谱的恒星在这个集群和周围的协会。从光谱类型的18个非常可能的成员协会和UBV测光发现在文献中，我们得出个人的红化，发现一个消光定律接近标准和平均距离模DM=13.0+-0.4。这个值是在很好的协议与距离模量的新集群阿利坎特1发现通过拟合光度序列的ZAMS。尽管有几颗O-型恒星存在，阿利坎特1是一个非常稀少的疏散星团，几乎完全没有早期的B-型恒星。我们的研究结果肯定了Cam OB 3位于天鹅臂上，并确定了第一个已知属于该协会的疏散星团。
The very flat radio - millimetre spectrum of Cygnus X-1
我们提出了几乎同时检测天鹅座X-1在无线电和毫米制度，在低/硬X射线状态。该源在2和220 GHz之间显示平坦的频谱，频谱指数平坦于0.15（3 sigma）。没有证据表明低频或高频截止，但在中红外（~30微米），来自OB型伴星的热辐射占主导地位。这种平谱发射在静止时的积分亮度大于2 x 10^{31} erg/s（2 x 10^{24} W）。假设发射起源于非辐射（例如绝热膨胀）损失占主导地位的射流，这是维持射流所需功率的非常保守的下限。与天鹅座X-3和GRS 1915+105相比，其他的X射线双星在短于厘米的波长下观察到平坦的光谱，表明天鹅座X-1的喷流明显不那么明亮，变化也较小，可能是我们迄今为止最好的例子，连续，稳定，从X射线双星流出。这种平坦光谱成分的发射机制仍然不确定。具体来说，我们注意到，从这些X射线双星观测到的无线电毫米光谱比那些“平谱”活动星系核平坦得多，现有的模型同步辐射部分自吸收的无线电核心，预测高频截止毫米政权，是不直接适用。
Stellar tracers of the Cygnus Arm I. Spectroscopic study of bright photometric candidates
我们提出了中等分辨率的光谱样本的恒星在银河系第二象限从文献中选择，因为他们的颜色表明，他们是适度变红的早期型恒星在非常大的距离。从衍生的光谱类型和观察到的颜色，我们计算到所有这些物体的距离。对于我们样本中相当大的一部分，我们发现距离远远超过了英仙座臂天体的预期，甚至允许相当慷慨的误差。在l= 150 degr-180 degr的区间内，有大量的距离超过4kpc的天体，它们很可能是在跟踪外旋臂或天鹅臂。特别是，我们发现关联Cam OB 3位于该旋臂上。基于我们的结果，关联Cas OB 4和Aur OB 2的范围和定义需要重新评估。
